1. Field of the Invention
The invention relates to a variable speed motor, more particularly to a variable speed motor with a tapped starting winding.
2. Description of the Related Art
Referring to FIGS. 1A and 1B, a variable speed motor for a ceiling fan in accordance with U.S. Pat. No. 4,841,188 is shown to include a motor body 5, a run coil 1, and a starting winding 2. The motor body 5, such as a stator, has an axis 510, and a plurality of coil mounting parts 511 that extend radially and that are angularly spaced apart relative to the axis 510, thereby forming a plurality of radial slots thereamong. The run coil 1 and the starting winding 2 are mounted on the coil mounting parts 511 of the motor body 5. As illustrated, the run coil 1 spans substantially all of the coil mounting parts 511 of the motor body 5. In addition, the coil mounting parts 511 are grouped into three adjacent clusters, each of which is spanned by a respective one of first, second and third speed-changing coils 205, 206, 207 of the starting winding 2. The starting winding 2 further includes a set of medium speed taps 203a, 203b, and a set of low speed taps 204a, 204b. 
The run coil 1 has first and second coil terminals 101, 102, and is to be connected across an AC power source 4. The first speed-changing coil 205 has a first coil terminal 201, and a second coil terminal provided with one of the medium speed taps 203a. The second speed-changing coil 206 has a first coil terminal provided with the other one of the medium speed taps 203b, and a second coil terminal provided with one of the low speed taps 204a. The third speed-changing coil 207 has a first coil terminal provided with the other one of the low speed taps 204b, and a second coil terminal 202. A capacitor 3 connects the second coil terminal 202 of the third speed-changing coil 207 to the second coil terminal 102 of the run coil 1.
During high-speed operation of the motor, the first coil terminal 201 of the first speed-changing coil 205 is connected to the first coil terminal 101 of the run coil 1, the medium speed taps 203a, 203b interconnect the first and second speed-changing coils 205, 206 in series, and the low speed taps 204a, 204b interconnect the second and third speed-changing coils 206, 207 in series. As such, the series combination of the first, second and third speed-changing coils 205, 206, 207 and the capacitor 3 is connected in parallel to the run coil 1 and to the AC power source 4.
Referring to FIGS. 2A and 2B, during medium-speed operation of the motor, the medium speed tap 203a connects the second coil terminal of the first speed-changing coil 205 to the first coil terminal 101 of the run coil 1, while the other medium speed tap 203b connects the first coil terminal of the second speed-changing coil 206 to the first coil terminal 201 of the first speed-changing coil 205. The low speed taps 204a, 204b interconnect the second and third speed-changing coils 206, 207 in series. As such, the series combination of the second and third speed-changing coils 206, 207 and the capacitor 3 is connected in parallel to the series combination of the first speed-changing coil 205 and the run coil 1 and to the AC power source 4.
Referring to FIGS. 3A and 3B, during low-speed operation of the motor, the medium speed taps 203a, 203b interconnect the first and second speed-changing coils 205, 206 in series. The low speed tap 204a connects the second coil terminal of the second speed-changing coil 206 to the first coil terminal 101 of the run coil 1, while the other low speed tap 204b connects the first coil terminal of the third speed-changing coil 207 to the first coil terminal 201 of the first speed-changing coil 205. As such, the series combination of the third speed-changing coil 207 and the capacitor 3 is connected in parallel to the series combination of the first and second speed-changing coils 205, 206 and the run coil 1 and to the AC power source 4.
Due to the arrangement of the starting winding 2, the directions of current flow through the first, second and third speed-changing coils 205, 206, 207 can be maintained when changing between high-speed and medium-speed operations, and when changing between medium-speed and low-speed operations, thereby resulting in noise reduction.
During the medium-speed and low-speed operations of the motor, at least one of the first and second speed-changing coils 205, 206 is connected in series to the run coil 1. As such, the amounts of currents flowing through the first, second and third speed-changing coils 205, 206, 207 of the starting winding 2 tend to differ from each other during the medium-speed and low-speed operations. Because the first, second and third speed-changing coils 205, 206, 207 span only a respective cluster of the coil mounting parts 511 of the motor body 5, uniform magnetic line distribution at the coil mounting parts 511 can not be maintained during the medium-speed and low-speed operations of the motor, which can affect stability and balance, and which can arise in the generation of vibration and noise.
Therefore, the main object of the present invention is to provide a variable speed motor with a tapped starting winding that is capable of overcoming the aforesaid drawback of the prior art.
According to this invention, a variable speed motor comprises a motor body, a run coil and a starting winding. The motor body has an axis, and a plurality of coil mounting parts that extend radially and that are angularly spaced apart relative to the axis. The run coil is mounted on the coil mounting parts. The starting winding includes first, second and third speed-changing coils mounted on the coil mounting parts, a set of first taps provided respectively on first and second coil terminals of the first speed-changing coil, a set of second taps provided respectively on first and second coil terminals of the second speed-changing coil, and a set of third taps provided respectively on first and second coil terminals of the third speed-changing coil. Each of the first, second and third speed-changing coils spans an angular length relative to the axis that is substantially equal to that spanned by the run coil.
Preferably, each of the run coil and the first, second and third speed-changing coils of the starting winding spans substantially all of the coil mounting parts of the motor body.